Django values_list vs values
DjangoDjango ModelsDjango QuerysetDjango OrmDjango Problem Overview
In Django, what's the difference between the following two:
Article.objects.values_list('comment_id', flat=True).distinct()
vs
Article.objects.values('comment_id').distinct()
My goal is to get a list of unique comment ids under each Article. I've read the documentation (and in fact have used both approaches). The results overtly seem similar.
Django Solutions
Solution 1 - Django
The values() method returns a QuerySet containing dictionaries:
<QuerySet [{'comment_id': 1}, {'comment_id': 2}]>
The values_list() method returns a QuerySet containing tuples:
<QuerySet [(1,), (2,)]>
If you are using values_list() with a single field, you can use flat=True to return a QuerySet of single values instead of 1-tuples:
<QuerySet [1, 2]>
Solution 2 - Django
values()
Returns a QuerySet that returns dictionaries, rather than model instances, when used as an iterable.
values_list()
Returns a QuerySet that returns list of tuples, rather than model instances, when used as an iterable.
distinct()
distinct are used to eliminate the duplicate elements.
Example:
>>> list(Article.objects.values_list('id', flat=True)) # flat=True will remove the tuples and return the list
[1, 2, 3, 4, 5, 6]
>>> list(Article.objects.values('id'))
[{'id':1}, {'id':2}, {'id':3}, {'id':4}, {'id':5}, {'id':6}]
Solution 3 - Django
You can get the different values with:
set(Article.objects.values_list('comment_id', flat=True))
Solution 4 - Django
The best place to understand the difference is at the official documentation on values / values_list. It has many useful examples and explains it very clearly. The django docs are very user freindly.
Here's a short snippet to keep SO reviewers happy:
values
> Returns a QuerySet that returns dictionaries, rather than model instances, when used as an iterable.
And read the section which follows it:
value_list
> This is similar to values() except that instead of returning dictionaries, it returns tuples when iterated over.